This invention relates to the electroplating of bright level nickel from aqueous solutions of nickel salts. More specifically it relates to bath additives useful as primary brighteners for improving the performance of such nickel electroplating solutions, and to baths and processes using such additives.
Prior art on the electroplating of nickel from aqueous solutions of nickel salts is considerable and well documented. Nickel deposits as plated from these baths such as the chloride, sulfamate, fluoborate and the well-known Watts baths are generally dull with a matte finish and of little value for commercial application. To obtain bright, level, ductile deposits from such baths it is necessary to add various addition agents or brighteners. Brightener agents useful in nickel plating are generally divided into two general classes on the basis of their predominant function. Classes of primary and secondary brighteners are well known in the art. Primary brighteners are materials used in relatively low concentrations of about 0.01 to 0.2 g/l which by themselves may or may not produce visible brightening action. In addition, deleterious side effects such as deposit brittleness, narrow bright plate range, and skip plating at low current densities may result. Secondary brighteners are materials which are used as brighteners in combination with primary brighteners but in higher concentrations, usually of about 1 to 20 g/l. Secondary brighteners by themselves may produce some brightening action but usually only over an inadequate current density range.
When primary and secondary brighteners are carefully selected, it is possible to obtain bright, level, ductile deposits over a wide current density range.
Modern processes relate mostly to the use of the Watts bath-13 an aqueous solution of nickel sulfate, nickel chloride and boric acid used in conjunction with a suitable additive system. The additive system usually comprises, as primary brighteners, highly polar or unsaturated compounds such as pyridinium salts or acetylenic alcohols; as secondary brighteners various organic sulfonic, sulfonamide and sulfonimide compounds as disclosed in U.S. Pat. Nos. 2,191,813 (1940) and 2,466,677 (1949) issued to Henry Brown generally are used. Among the more favored secondary brighteners are saccharin and its sodium or potassium salts, sodium allyl sulfonate, naphthalene di- and tri-sulfonic acids, dibenzenesulfonimide and sodium 3-chlorobutene 1-sulfonate. Mixtures of these secondary brighteners are frequently employed. Acetylenic alcohols or their derivatives are now generally preferred as primary brighteners since they show less tendency to form brittle deposits and control of their concentration in the bath is less critical. One of the most preferred because of performance, availability and low cost in 2-butyne 1,4-diol, discussed in U.S. Pat. No. 2,712,522 issued to Otto Kardos et al. in 1955.
Use of 2-butyne 1,4-diol in conjunction with secondary brighteners of the type described above in the Watts bath yields lustrous, levellel deposits with good ductility, but there is a tendency for the formation of pitted deposits together with dark thin plate and skipped or missed plating at low current densities. To minimize these problems, derivatives of 2-butyne 1,4-diol are frequently used. Among the more favored are hydroxyalkyl derivatives obtained by the base-catalyzed addition of various epoxides to 2-butyne 1,4-diol as disclosed by Foulke et al. in U.S. Pat. No. 3,366,557 (1968). Addition of more than about 2 or 3 moles of epoxide per mole of butyne diol, while alleviating the low current density problems, tends also to result in undesirable loss of brightening or levelling ability. Similarly, acetylenic alcohols of higher molecular weight than butyne diol, while operable, are generally less effective. Symmetrical hydroxyalkyne sulfonates obtained by the acid-catalyzed reaction of acetylenic diols with epihalohydrins followed by conversion of the halide grouping to a sulfonate grouping by reaction with sodium sulfite are disclosed in U.S. Pat. No. 3,699,016 issued to Beach et al. in 1972. In conjunction with aromatic sulfur compounds as secondary brighteners these compounds give good overall performance, although there appears to be some tendency for some of them to produce a white haze at high current densities.
Consequently, it is an object of this invention to provide new compositions of matter comprising mixtures of alkyne compounds which, when used in conjunction with suitable secondary brighteners, act synergistically one upon the other to produce bright, level and ductile nickel over a wide current density range extending from high into very low current density areas.